1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device for use in micromachines and to a method of producing the semiconductor.
2. Background Information
Micromachine technology has been proposed in the past that employs semiconductor materials such as silicon and the like. Devices that employ micromachine technology include fluid control devices such as sensors, microactuators, micropumps, and valves. With these types of devices, insulating film or metal patterns are generally used on the surface of the semiconductor substrate to form three dimensional structures.
FIG. 15 shows the structure of a micropump and the principles of its operation. FIG. 15(A) shows a discharge mode of the micropump, FIG. 15(B) shows a discharge mode of the micropump, FIG. 15(C) is a plan view of the valves, the inlet, and the outlet of the micropump, and FIG. 15(D) is an enlarged view of a valve. The micropump is comprised of a heat resistant glass plate 601 in which a diaphragm 602 is formed, a silicon substrate 701 in which valves 702a, 702b and through holes 703a, 703b, 703c, 703d (through holes 703) are formed, and a heat resistant glass plate 801 that is bonded to the surface of the silicon substrate that is opposite the side of the silicon substrate that is bonded to the heat resistant glass plate 601. A piezoactuator 603 is arranged on top of the diaphragm 602 of the heat resistant glass plate 601, and serves to oscillate the diaphragm 602. The valves 702a, 702b are formed on top of the silicon substrate 701 having the through holes 703 therein, and the through holes 703 serve as fluid pathways. The valves 702a, 702b are formed from disk-shaped valves made of polysilicon that are shaped so that they close the fluid pathways, and four arms that are fixed to the substrate on one side thereof and support the valves (see FIG. 15(C), (D)).
A micropump having this type of structure is operated by applying a voltage to the piezoactuator 603. The piezoactuator 603 to which a voltage has been applied pushes the diaphragm 602 downward. Thus, the pressure inside a pressure chamber 606 increases, the valve 702a on the inlet 604 closes, the valve 702b on the outlet 605 opens, and liquid is discharged from the outlet 605 (see FIG. 15(A)). When the voltage is switched off, the diaphragm 602 returns to its original position. Thus, the pressure inside the pressure chamber 606 decreases, the valve 702b on the outlet 605 closes, the valve 702a on the inlet 604 opens, and new liquid is drawn into the pressure chamber 606 (see FIG. 15(B)).
In a method of producing this type of micropump, after the valves 702a, 702b are formed on the silicon substrate 701, the through holes 703b, 703d are formed such that their position precisely matches the positions of the valves 702. In addition, the through holes 703a, 703c are formed so that their positions precisely match the positions of the inlet 604 and the outlet 605 formed in the heat resistant glass plate 601. The through holes 703 are formed by forming masks on both sides of the silicon substrate 701, and anisotropic etching the silicon substrate 701 from the upper and lower surfaces thereof.
However, the thickness of the silicon or other semiconductor substrate is, for example, approximately 625 micrometers if the substrate is a 6 inch wafer, and deep etching is performed on the substrate. Because of that, the direction in which etching proceeds will differ until the through hole formed thereby passes through the upper surface or the lower surface of the semiconductor substrate, and thus it is difficult to place a through hole in a desired position on a surface of the substrate. It is thought that this is due to the following reasons:
(1) Although the alignment of a position on the upper surface of a substrate that a through hole must pass through with a position on the lower surface of the substrate where etching is initiated is performed by means of image processing, it is difficult to obtain a precise alignment due to deviation in the image process.
(2) Deviation is produced in the direction in which etching proceeds due to lattice defects that exist in the semiconductor substrate, and thus the position of an opening on the upper surface thereof will deviate from the desired position.
(3) When there are large fluctuations in etching speed due to temperature and/or humidity, and when batch processing is performed, it is difficult to control irregularities in the etching speed and the amount of side etching that occurs inside the wafer and on the surface thereof.
Because of that, one has no choice but to design a semiconductor device in which the position and the size of each opening of a through hole formed in the surface of the semiconductor substrate have a margin, which will make the size of the semiconductor device larger and increase its cost of production. More specifically, even when one wants to employ a 6 inch silicon substrate and form through holes 20 micrometers in width in the surface thereof, it is estimated that a 100 micrometer space for each opening will be required during the production steps.
An object of the present invention is to form through holes having good precision in one surface of a semiconductor substrate from another surface thereof.
Another object of the present invention is to produce and provide a highly precise semiconductor device by forming through holes having openings with the required size in a surface of the semiconductor substrate from another surface thereof.
Yet another object of the present invention is to produce a semiconductor device having a consistent quality by consistently forming through holes therein regardless of the wafer or the production process employed.